Research has shown that a large proportion of male fish in some British rivers are changing sex through exposure to pollutants.

Chemicals from sewage treatment plants and factories are causing male fish to produce eggs. The chemicals act like the hormone, oestrogen, which is normally produced in the ovaries of female animals.

The Environment Agency and scientists from Brunel University examined 2000 male roach taken from eight rivers.

The cells of a normal testis give way to the darker stained cells of a female

They found that between 25% and 60% of them had produced eggs in their testes, and in some sites downstream of sewage treatment plants, all male fish had an 'inter-sex condition'.

Although it was already known that oestrogen in river water could feminise male fish, the researchers said they were surprised by the extent and severity of the effect.

According to the agency it is now clear that effluent from sewage treatment plants does contain substances that change the hormones in fish, although further research is needed to determine exactly which pollutants are responsible for the changes.

Oestrogen-type substances exert a powerful effect at very low concentrations and fears have been raised that small amounts could find their way into domestic water supplies.

Dr Jean Ginsburg, a hormone specialist, said that any possibility of such substances entering the food chain is reason enough to implement tougher standards.

Dr Jean Ginsburg: we should take steps to prevent it entering the food chain

"What we ought to be doing is adopting what is called the precautionary principle," she said.

"That means [that] when there is sufficient evidence for cause for alarm, we take steps to avoid it."

The Environment Agency says it now wants water companies to investigate ways of removing oestrogen-type substances from effluent.

Jan Pentreath, from the agency, said: "We want the water industry to look at this carefully and see if there is something they can do.

"We want industry to consider ways of phasing [the chemicals] out, finding alternatives, or at the very least minimising the risk of them entering the environment."
 

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